Oxygen Barrier Properties
Yes, custom mylar bags are exceptionally suitable for long-term food preservation, primarily due to their superior oxygen barrier. The fundamental enemy of stored food is oxygen, which facilitates oxidation and supports the life processes of insects and aerobic microorganisms. Mylar, a brand name for BoPET (Biaxially-oriented Polyethylene Terephthalate), is a polyester film known for its exceptional gas and moisture barrier qualities. A standard mylar bag used for food storage typically has an oxygen transmission rate (OTR) of less than 0.05 cc/m²/24hrs at 23°C and 0% relative humidity. To put this in perspective, compare it to other common packaging materials:
Oxygen Transmission Rate (OTR) Comparison
| Material | Approximate OTR (cc/m²/24hrs) | Suitability for 25-Year Storage |
|---|---|---|
| Mylar (3.5 mil / 90 microns) | < 0.05 | Excellent |
| Polyethylene (PE) Plastic | 100 - 200 | Poor (Months) |
| Polypropylene (PP) Plastic | 50 - 100 | Poor (Months) |
| Food-Grade Bucket (HDPE) | 100 - 150 | Fair (1-2 Years with liner) |
This incredibly low OTR is what allows properly sealed mylar bags to achieve a shelf life of 10, 20, or even 25+ years for low-moisture foods. When you combine the bag with oxygen absorbers, the oxygen level inside the sealed pouch can drop below 0.01%, effectively creating an anaerobic environment that halts oxidation and prevents the growth of pests and spoilage organisms.
Moisture and Light Protection
Beyond oxygen, moisture and light are the other two critical factors that degrade food quality over time. Mylar bags provide an almost impenetrable shield against both. Their moisture vapor transmission rate (MVTR) is exceptionally low, typically below 0.05 g/m²/24hrs. This means humidity fluctuations in your storage environment have virtually no effect on the food inside the bag, protecting it from becoming stale or clumping and preventing the activation of mold spores.
Furthermore, mylar is naturally opaque. This light-blocking property is crucial for preserving the nutritional content of food. Light, especially UV light, acts as a catalyst for chemical reactions that break down vitamins (like A, B2, Riboflavin, and C) and cause fats to become rancid. By storing food in the dark interior of a mylar bag, you significantly slow these degradation processes. For optimal protection, it's recommended to store the sealed mylar bags themselves in a dark, cool place, such as a food-grade bucket or a cupboard, which adds an extra layer of security against light and physical damage. When you're looking for a supplier that understands these technical requirements, a custom mylar bag manufacturer with experience in food-grade materials is essential.
The Critical Role of Thickness (Mil/Microns)
Not all mylar bags are created equal. Their performance is directly tied to their thickness, measured in "mils" (thousandths of an inch) or microns. Thicker bags offer greater durability and a marginally better barrier, which becomes important for very long-term storage or for foods with sharp edges that could potentially puncture a thinner bag.
Mylar Bag Thickness Guide
| Thickness | Common Uses | Durability |
|---|---|---|
| 3.5 mil (90 microns) | The industry standard for long-term (25+ year) food storage. Ideal for grains, beans, pasta. | Excellent puncture resistance. |
| 4.5 mil (114 microns) | Heavy-duty storage. Good for foods with sharper edges like dehydrated apple slices or macaroni. | Superior puncture resistance. |
| 5.0 mil (127 microns) and above | Less common, used for maximum durability or non-food items requiring extreme barriers. | Maximum durability, less flexible. |
For the vast majority of home food storage applications, a 3.5 mil bag is more than sufficient. The key is to ensure the bags are made from food-grade, FDA-compliant materials, as lower-quality mylar films might contain chemical additives that could leach into your food over decades.
Foods Best Suited for Mylar Bag Storage
Mylar bags are incredibly versatile, but they excel with specific types of dry goods. The golden rule is that the food must be dry—typically with a moisture content of 10% or less. Storing moist foods can lead to botulism risk, as the anaerobic environment can favor the growth of Clostridium botulinum bacteria.
Ideal Candidates:
- Grains: Wheat, rice (white, brown, jasmine), oats, corn, quinoa. White rice can last 25-30 years, while brown rice, due to its higher oil content, has a shorter shelf life of 5-10 years even in mylar.
- Legumes: Beans (pinto, black, kidney), lentils, peas. These can easily last 20-25 years.
- Flours: White flour, whole wheat flour. Whole wheat flour has a shorter shelf life (5-10 years) due to the germ oil.
- Pasta: All dry pasta forms.
- Dehydrated and Freeze-Dried Foods: Fruits, vegetables, and even dairy powders. These are perfect for mylar as they are already low in moisture.
- Sugar and Salt: These are natural preservatives themselves and become virtually immortal when stored in mylar.
- Powdered Milk: Non-fat varieties store best.
Foods to Avoid:
- High-moisture foods (fresh fruits/vegetables).
- High-oil content foods (nuts, whole-grain cornmeal, brown rice) have a shorter shelf life (5-10 years) due to the risk of oils turning rancid, though mylar still extends their life significantly compared to other methods.
- Foods packaged in paper or cardboard that may contain insect eggs. Freezing these items for a week before sealing in mylar can eliminate this risk.
The Sealing Process: Heat Impulse Sealers vs. Household Irons
The effectiveness of a mylar bag is entirely dependent on achieving a perfect, airtight seal. There are two primary methods, with a significant difference in reliability.
1. Heat Impulse Sealer: This is the professional and recommended tool. It works by applying a burst of heat and pressure to a specific area of the bag's opening, melting the polyethylene layer on the inside of the mylar bag and fusing it together. The seal is strong, consistent, and less prone to failure. Industrial sealers can create seals up to 20 inches wide or more, while affordable 12-inch and 16-inch models are perfect for home use. A proper seal should be about 1/2 inch wide and be smooth and uniform, with no wrinkles or gaps.
2. Household Iron or Flat Iron: This is a common DIY method but carries a high risk of failure. The iron's heat is not as controlled or focused, leading to potential weak spots, incomplete seals, or even melting through the bag. If you must use this method, place a piece of parchment paper or a silicone sheet over the bag's opening to protect it, use a medium heat setting, and press firmly, slowly moving the iron across the width. However, for any serious long-term storage investment, a dedicated sealer is a non-negotiable tool for ensuring the integrity of your food supply.
Integrating Oxygen Absorbers: The Perfect Partnership
While mylar is a fantastic oxygen barrier, the air trapped inside the bag during sealing contains about 21% oxygen. This is where oxygen absorbers become essential. These small packets contain iron powder, which rusts (oxidizes) when exposed to the air, chemically binding the oxygen molecules. The size of the absorber you need is determined by the volume of air left in the bag after you've filled it with food. A general guideline is to use 100cc to 300cc of oxygen absorber capacity for a one-gallon mylar bag, and 500cc to 1500cc for a five-gallon bag. Using too small an absorber means not all oxygen is removed; using too large is generally not a problem, as the absorber will simply become inert once all oxygen is consumed. You'll know it worked when the bag becomes rigid and vacuum-packed-looking a few hours after sealing, as the oxygen removal creates a slight vacuum.
Cost-Effectiveness and Practicality
From a financial and space-management perspective, mylar bags are highly efficient. Compared to #10 cans, which are the other gold standard for long-term food storage, mylar bags are significantly less expensive per unit of volume and are lightweight and flexible, allowing you to pack them efficiently into larger containers like 5-gallon buckets. This "bag-in-a-bucket" method provides the oxygen and light barrier of the mylar, plus the physical protection and stackability of the bucket. Once sealed, mylar bags are also resistant to pests like rodents and insects. Furthermore, the portioning flexibility is a major advantage; you can pack a 5-gallon bucket with several smaller one-gallon mylar bags, allowing you to open a single gallon of rice or beans at a time without exposing your entire stock to oxygen and moisture, which is a limitation of a single large #10 can or an open bucket.